1. Field of the Invention
The present invention relates to a dispersion compensation device adapted to compensate for waveform distortion of an optical signal using a variable dispersion compensation compensator and capable of long-distance, large-volume transmission.
2. Description of the Related Art
The speed of signals accommodated in a wavelength division multiplexer has been increased from 10 Gpbs to 40 Gbps in order to address the communication traffic in recent years. As the speed of optical signals subject to multiplexing becomes higher, the signals are more likely to be affected by distortion (dispersion) occurring in optical signal pulses on a transmission line. This will require high-precision dispersion compensation technology for canceling the effects from dispersion.
Conventional 10 Gbps signals that are wavelength-multiplexed by a wavelength multiplexer can be received properly by collectively subjecting the signals to dispersion compensation using a dispersion compensation fiber. As the speed of signals is increased to 40 Gbps, however, the dispersion tolerance of the receiving end becomes extremely low. In this regard, it has become necessary to subject signals of individual wavelengths derived from wavelength division to dispersion compensation using a variable dispersion compensator as well as collectively subjecting signals that are wavelength-multiplexed to dispersion compensation. In one known method of controlling a variable dispersion compensator, the bit error rate of a received data signal is monitored and the dispersion compensation value of the variable dispersion compensator is set so that the bit error rate is minimized (see, for example, patent document No. 1).
[patent document No. 1] JP 2002-208892
In the case of the approach of patent document No. 1 whereby the dispersion compensation value is set based on the bit error rate, however, there is a problem in that the setting of an optimal dispersion compensation values takes a very long time. In other words, it takes a long time to search for a dispersion compensation value that minimizes the bit error rate while varying the dispersion compensation value over the entire range of dispersion compensation of the variable dispersion compensator. In particularly, the dispersion tolerance at the receiving end of optical signals becomes poor in response to high-speed optical signals such as 40 Gbps signals. Therefore, since the dispersion compensation value has to be varied in very small steps in order to identify an optimal dispersion compensation value that minimizes the bit error rate, an enormous amount of time is required to control the dispersion compensation value.